Imaging Findings

Computed Tomography (CT) showed a voluminous 7x9 cm aneurysm of the sub-renal abdominal aorta with a cranio-caudad extension of approximately 10 cm, up to the aortic bifurcation, partially thrombosed (Fig. 1). The presence of air bubbles within the aorta’s parietal thrombus (Fig. 2, 3) allowed to diagnose a primary aorto-duodenal fistula (PADF), communicating with the duodenal inferior angle. A retroperitoneal haematoma was seen along the left psoas muscle (Fig. 2).

Discussion

Primary aorto-duodenal fistula (PADF) is defined as communication between the aorta and the duodenum, in the absence of any previous vascular intervention. Secondary aortoduodenal fistulae occur most commonly after reconstructive aortic surgery. Aortoenteric fistulae in the larger sense may involve any portion of the gut from the oesophagus to the colon [1]. Aortoduodenal fistulae comprise 80% of all aortoenteric fistulae [2], due to the anatomical proximity between the third portion of the duodenum and the underlying aorta [3].PADF results most commonly out of an underlying atherosclerotic aortic aneurysm. Other conditions that may lead to PADF include radiation therapy, aortitis (syphilis, tuberculosis), tumours, peptic ulcers, and collagen vascular disease [2, 4].Clinical features include the classic triad of gastrointestinal bleeding, abdominal pain and a pulsating abdominal mass. Other symptoms such as back pain, melaena and fever are sometimes found. A “herald bleed” may precede lethal haemorrhage. Early recognition of the condition is important because of the very high mortality rate if left untreated.Triple-phase CT is the imaging investigation of choice in diagnosing PADF. CT findings include retroperitoneal gas, gas within the aortic parietal thrombus or within the perfused lumen, obliteration of the fat stripe that normally separates the aorta from the duodenum, and contrast extravasation into the duodenum or a perianeurysmatic haematoma [1-4].Oesophagogastroduodenoscopy is often readily available and performed to identify other causes of upper gastrointestinal bleeding [5], but a negative endoscopy does not rule out PADF.Surgical treatment of PADF consists of repair of the duodenal breach and performing prosthetic repair of the aorta (Dacron® or polytetrafluoroethylene graft) [3] versus homograft implantation, as it was the case for our patient. A clinical suspicion of PADF without imaging confirmation requires exploratory laparotomy.

Conclusion: PADF is a rare cause of gastrointestinal bleeding. The diagnosis has to be considered if clinical suspicion is high and no other source of gastrointestinal bleeding is identifiable. PADF has a very high mortality rate if left untreated. Diagnosis is usually made by CT. Oesophagogastroduodenoscopy is useful to rule out other causes of gastrointestinal haemorrhage. Early surgical intervention improves the chances of successful management of aorto-duodenal fistula.

Area of Interest:Cardiovascular system; Imaging Technique:CT; Procedure:Contrast agent-intravenous; Special Focus:Aneurysms;

Figure 2

Axial contrast-enhanced CT

Obliteration of the fat stripe that normally separates the abdominal aorta from the duodenum (yellow arrow). Intraaortic air bubbles are seen (red arrowhead). Note also the retroperitoneal haematoma along the left...

Area of Interest:Cardiovascular system; Imaging Technique:CT; Procedure:Contrast agent-intravenous; Special Focus:Aneurysms;

Obliteration of the fat stripe that normally separates the abdominal aorta from the duodenum (yellow arrow). Intraaortic air bubbles are seen (red arrowhead). Note also the retroperitoneal haematoma along the left psoas muscle (yellow arrowhead).